Analog Electronics – Page 36
Bode Plot and Bandwidth of Amplifiers
A Bode plot is a graphical representation of amplifier gain versus frequency on a logarithmic scale.
It helps engineers understand how amplifier gain changes over different frequencies.
What is a Bode Plot?
- Frequency is plotted on logarithmic scale
- Gain is plotted in decibels (dB)
- Shows amplifier frequency response clearly
Gain(dB) = 20 log₁₀(Av)
Important Frequency Points
- Lower cutoff frequency → fL
- Upper cutoff frequency → fH
- Midband region → constant gain
Bandwidth
Bandwidth is the frequency range where the amplifier gain remains approximately constant.
Bandwidth (BW) = fH − fL
Slope of Bode Plot
At cutoff frequencies, gain begins to decrease.
- Single pole system → −20 dB/decade
- Two pole system → −40 dB/decade
Example Problem
If an amplifier has:
- Lower cutoff frequency fL = 200 Hz
- Upper cutoff frequency fH = 200 kHz
Find bandwidth.
BW = fH − fL
BW = 200000 − 200
BW ≈ 199.8 kHz
Important GATE Points
- Bode plot uses logarithmic frequency scale
- Gain expressed in decibels
- Cutoff occurs at 0.707 of midband gain
- Slope is −20 dB/decade for single pole systems
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